Microwave antenna having a reactively-loaded loop configuration

ABSTRACT

A microwave ablation system is provided. The microwave ablation system includes a power source. A microwave antenna is adapted to connect to the power source via a coaxial cable feed including an inner conductor defining a portion of a radiating section of the microwave antenna, an outer conductor and dielectric shielding. The inner conductor loops back around and toward the outer conductor of the coaxial cable feed such that a distal end of the inner conductor is operably disposed adjacent the dielectric shielding. The inner conductor includes one or more reactive components disposed thereon forming a reactively-loaded loop configuration configured to maximize delivery of microwave energy from the power source to tissue such that a desired effect to tissue is achieved.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation application of U.S. patentapplication Ser. No. 12/826,902 filed on Jun. 30, 2010, the entirecontents of which are incorporated by reference herein.

BACKGROUND

1. Technical Field

The present disclosure relates to microwave antennas. More particularly,the present disclosure relates to microwave antennas having areactively-loaded loop configuration defining a portion of a radiatingsection of the microwave antenna.

2. Background of Related Art

Microwave ablation procedures, e.g., such as those performed formenorrhagia, are typically done to ablate the targeted tissue todenature or kill the tissue. Many procedures and types of devicesutilizing electromagnetic radiation therapy are known in the art. Suchmicrowave therapy is typically used in the treatment of tissue andorgans such as the prostate, heart, and liver.

One non-invasive procedure generally involves the treatment of tissue(e.g., a tumor) underlying the skin via the use of microwave energy. Themicrowave energy is able to non-invasively penetrate the skin to reachthe underlying tissue. Typically, microwave energy is generated by apower source, e.g., microwave generator, and transmitted to tissue via amicrowave antenna that is fed with a coaxial cable that operably couplesto a radiating section of the microwave antenna.

For optimal energy delivery efficiency from the microwave generator tothe microwave antenna, impedance associated with the coaxial cable, theradiating section and/or tissue need to equal to one another, i.e., animpedance match between the coaxial cable, the radiating section and/ortissue. In certain instances, an impedance mismatch may be presentbetween the coaxial cable, the radiating section and/or tissue, and theenergy delivery efficiency from the microwave generator to the microwaveantenna is compromised, e.g., decreased, which, in turn, may compromisea desired effect to tissue, e.g., ablation to tissue.

SUMMARY

The present disclosure provides a microwave ablation system. Themicrowave ablation system includes a power source. A microwave antennais adapted to connect to the power source via a coaxial cable feedincluding an inner conductor defining a portion of a radiating sectionof the microwave antenna, an outer conductor and dielectric shielding.The inner conductor loops back around and toward the outer conductor ofthe coaxial cable feed such that a distal end of the inner conductor isoperably disposed adjacent the dielectric shielding. The inner conductorincludes one or more reactive components disposed thereon forming areactively-loaded loop configuration.

The present disclosure provides a microwave antenna adapted to connectto a power source for performing a microwave ablation procedure. Themicrowave antenna includes a coaxial cable feed including an innerconductor defining a portion of a radiating section of the microwaveantenna, an outer conductor and dielectric shielding. The innerconductor loops back around and toward the outer conductor of thecoaxial cable feed such that a distal end of the inner conductor isoperably disposed adjacent the dielectric shielding. The inner conductorincludes one or more reactive components disposed thereon forming areactively-loaded loop configuration.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features, and advantages of the presentdisclosure will become more apparent in light of the following detaileddescription when taken in conjunction with the accompanying drawings inwhich:

FIG. 1A is a perspective view of a microwave ablation system adapted foruse with a microwave antenna that utilizes a reactively-loaded loopconfiguration according to an embodiment of the present disclosure;

FIG. 1B is a perspective view of another type of microwave antenna thatutilizes a reactively-loaded loop configuration according to anembodiment of the present disclosure and is adapted for use with themicrowave ablation system depicted in FIG. 1A;

FIG. 2A is partial, cut-away view of a distal tip of the microwaveantenna depicted in FIG. 1B illustrating a radiating section associatedwith microwave antenna;

FIG. 2B is a cross-section view taken along line segment “2B-2B”illustrated in FIG. 2A;

FIG. 3 is partial, cut-away view of the distal tip of the microwaveantenna depicted in FIG. 1B illustrating an alternate embodiment of theradiating section depicted in FIG. 2A;

FIG. 4 is partial, cut-away view of the distal tip of the microwaveantenna depicted in FIG. 1B illustrating a conductive shield operablypositioned adjacent the radiating section depicted in FIG. 2A;

FIG. 5 is partial, cut-away view of the distal tip of the microwaveantenna depicted in FIG. 1B illustrating a conductive shield operablypositioned adjacent the radiating section depicted in FIG. 2A accordingto an alternate embodiment of the present disclosure; and

FIG. 6 is partial cut-away view of the distal tip of the microwaveantenna depicted in FIG. 1B illustrating a conductive shield operablypositioned adjacent the radiating section depicted in FIG. 2A accordingto another embodiment of the present disclosure.

DETAILED DESCRIPTION

Embodiments of the presently disclosed microwave antenna are describedin detail with reference to the drawing figures wherein like referencenumerals identify similar or identical elements. As used herein and asis traditional, the term “distal” refers to the portion which isfurthest from the user and the term “proximal” refers to the portionthat is closest to the user. In addition, terms such as “above”,“below”, “forward”, “rearward”, etc. refer to the orientation of thefigures or the direction of components and are simply used forconvenience of description.

Referring now to FIG. 1A, a microwave ablation system 10 adapted for usewith a microwave antenna 100 that utilizes a reactively-loaded loopconfiguration according to an embodiment of the present disclosure isillustrated. The system 10 includes microwave antenna 100 that isadapted to connect to an electrosurgical power source, e.g., an RFand/or microwave (MW) generator 200 that includes or is in operativecommunication with one or more controllers 300 and, in some instances, afluid supply pump 40. Briefly, microwave antenna 100 includes anintroducer 116 having an elongated shaft 112 and a radiating orconductive tissue piercing tip 114 operably disposed within elongatedshaft 112, a cooling assembly 120 having a cooling sheath 121, a handle118, a cooling fluid supply 122 and a cooling fluid return 124, and anelectrosurgical energy connector 126. Connector 126 is configured toconnect the microwave antenna 100 to the electrosurgical power source200, e.g., a generator or source of radio frequency energy and/ormicrowave energy, and supplies electrosurgical energy to the distalportion of the microwave antenna 100. Conductive tip 114 and elongatedshaft 112 are in electrical communication with connector 126 via aninternal coaxial cable 126 a that extends from the proximal end of themicrowave antenna 100 and includes an inner conductor 126 b (shown inphantom) operably disposed within the shaft 112 and adjacent a radiatingsection 138 (shown in phantom) and/or the conductive or radiating tip114. As is common in the art, the internal coaxial cable 126 a includesa dielectric material and an outer conductor surrounding each of theinner conductor 126 b and the dielectric material. A connection hub (notexplicitly shown) disposed at a proximal end of the microwave antenna100 operably couples connector 126 to internal coaxial cable 126 a, andcooling fluid supply 122 and a cooling fluid return 124 to a coolingassembly 120. Radiating section 138 by way of conductive tip 114 (or incertain instances without conductive tip 114) is configured to deliverradio frequency energy (in either a bipolar or monopolar mode) ormicrowave energy to a target tissue site. Elongated shaft 112 andconductive tip 114 may be formed of suitable conductive materialincluding, but not limited to copper, gold, silver or other conductivemetals having similar conductivity values. Alternatively, elongatedshaft 112 and/or conductive tip 114 may be constructed from stainlesssteel or may be plated with other materials, e.g., other conductivematerials, such as gold or silver, to improve certain properties, e.g.,to improve conductivity, decrease energy loss, etc. In an embodiment,the conductive tip 114 may be deployable from the elongated shaft 112.

With reference now to FIG. 1B, a microwave antenna 512 that utilizes areactively-loaded loop configuration according to an embodiment of thepresent disclosure and adapted for use with the microwave ablationsystem depicted in FIG. 1A is illustrated. Briefly, microwave antenna512 operably couples to generator 200 including a controller 300 via aflexible coaxial cable 516. In this instance, generator 200 isconfigured to provide microwave energy at an operational frequency fromabout 300 MHz to about 10 GHz. Microwave antenna 512 includes aradiating section or portion 518 that may be connected by a feedline orshaft 520 to coaxial cable 516 that extends from the proximal end of themicrowave antenna 512 and includes an inner conductor operably disposedwithin the shaft 520 and adjacent radiating section 518 and/or aconductive or radiating tissue piercing tip 524. More specifically, themicrowave antenna 512 is coupled to the cable 516 through a connectionhub 522. The connection hub 522 also includes an outlet fluid port 530(similar to that of cooling fluid return 124) and an inlet fluid port532 (similar to that of cooling fluid supply 122) that are connected influid communication with a sheath 538. The sheath 538 encloses theradiating portion 518 and the shaft 520 allowing for coolant fluid fromthe ports 530 and 532 to be supplied to and circulated around theantenna assembly 512 via respective fluid lumens 530 a and 532 a. Theports 530 and 532 may also couple to supply pump 40. For a more detaileddescription of the microwave antenna 512 and operative componentsassociated therewith, reference is made to commonly-owned U.S. patentapplication Ser. No. 12/401,268 filed on Mar. 10, 2009.

With reference to FIG. 2A, a reactively-loaded loop configuration (“loop400”) according to an embodiment of the present disclosure is shown anddesignated 400. As defined herein, “reactively-loaded” is meant to meanincluding an element or component that opposes alternating current,caused by a build up of electric or magnetic fields in the element orcomponent due to the current. Loop 400 may be operably associated witheither of the radiating sections 138 or 518. For illustrative purposesloop 400 is described in terms of the radiating section 518 associatedwith the microwave antenna 512. Loop 400 is constructed by extending aninner conductor 516 a, associated with the coaxial cable 516 distallypast a dielectric material 516 b and an outer conductor 516 c. The innerconductor 516 a is looped around and back toward the outer conductor 516c of the coaxial cable 516 such that a radiating section 518 having agenerally “loop” like configuration is formed, the significance of whichis described in greater detail below. In embodiments, loop 400 includesa diameter that ranges from about 3 mm to about 15 mm. Inner conductor516 a may have any suitable configuration including but not limited towire, strip, etc. In the illustrated embodiments, inner conductor 516 aincludes a wire configuration having a diameter that ranges from about0.0010 inches to about 0.0020 inches. In the instance where the innerconductor 516 a includes a strip configuration, the strip may include awidth that ranges from about 0.0010 inches to about 0.0020 inches. Tooptimize electrosurgical energy transfer from the generator 200 to themicrowave antenna 512 it is important that an impedance match be presentbetween coaxial cable 516, radiating section 518 and tissue at a targettissue site. In accordance with the present disclosure, a length of theloop 400 is configured for tuning, i.e., impedance matching, animpedance associated with the inner conductor 516 a, microwave antenna512 and tissue at a target tissue site such that optimal transfer ofelectrosurgical energy is provided from the generator 200 to theradiating section 518 such that a desired tissue effect is achieved at atarget tissue site.

With continued reference to FIG. 2A, one or more reactive elements orcomponents are operably disposed along a length of loop 400 associatedwith the inner conductor 516 a to achieve a desired electrical effect atthe radiating section 518. In the embodiment illustrated in FIG. 2A, oneor more coiled sections 402 (one coiled section is shown forillustrative purposes) that serves as an inductive component is formed(or in some instances positioned, such as, for example, when aninductive component is utilized) adjacent a proximal end of the innerconductor 516 a. The coiled section 402 may include any number ofsuitable turns such that a desired voltage may be induced therein by anelectromagnetic field present in the coiled section 402 whenelectrosurgical energy is transmitted to the microwave antenna 512 and,more particularly, to the radiating section 518. One or more capacitivecomponents 404 (three capacitive components are shown for illustrativepurposes) are operably disposed at distal end of the loop 400 and/orinner conductor 516 a. More particularly, capacitive components 404 arepositioned adjacent outer conductor 516 c and/or dielectric material 516b. The capacitive components 404 are in the form of three capacitordisks 404 that function to provide a capacitive effect at the distal endof the loop 400 when the distal end of the loop 400 is positionedadjacent (or contacts) the outer conductor 516 c and/or the dielectricmaterial 516 b. The inductive and capacitive components 402 and 404,respectively, may be arranged in any suitable electrical configuration,i.e., series or parallel.

In the embodiment illustrated in FIG. 2A, the inductive and capacitivecomponents 402 and 404, respectively, are arranged in series withrespect to each other. In an alternate embodiment, the respectiveinductive and capacitive components 402 and 404 may be arranged in aparallel configuration with respect to each other. That is, innerconductor 516 a may be split into two branches forming a parallelconfiguration, wherein each branch includes a respective reactivecomponent. More particularly, one branch may include one or moreinductive components 402 and one branch may include one or morecapacitive component 404. To achieve desired capacitive or inductiveeffects at the loop 400 formed by the inner conductor 516 a, a thicknessof the inner conductor 516 a may varied (i.e., increased or decreased)as needed. Loading the loop 400 with one or more reactive componentsdescribed herein enables the radiating section 518 to be shortened orlengthened during the manufacturing process such that a desiredelectrical effect (e.g., impedance) or output may be achieved at theradiating section 518 and/or conductive tip 524. Additionally, reactiveloading of the loop 400 allows for miniaturization of the radiatingsection 518, which, in turn, provides for a more practical invasivemicrowave antenna 512 and/or radiating section 518.

In an alternate embodiment, see FIG. 3, the loop 400 may include aspiral loop configuration. In this instance, the loop 400 includes oneor more spiral sections 406 that provide one or more reactive effects,e.g., an inductive effect described above. Not unlike the loop 400illustrated in FIG. 2A, a distal end of the spiral section 406 of loop400 and/or the inner conductor 516 a is positioned adjacent (orcontacts) the outer conductor 516 c and/or the dielectric material 516b. While not explicitly shown, it is within the purview of the presentdisclosure that one or more of the reactive components described above,e.g., an inductive component 402 and/or a capacitive component 404, maybe operably disposed within the electrical path of the spiral section406 of the loop 400. That is, the inductive component 402 and/or acapacitive component 404 may be arranged in series or parallelconfigurations with respect to each other and/or the spiral section 406of loop 400.

In one particular embodiment, one or more structure(s) or device(s) maybe employed to concentrate the electrosurgical energy radiating from theradiating section 518 and/or conductive tip 524 to tissue at a targettissue site. More particularly, and with reference to FIG. 4, areflector or shield 408 may be operably positioned adjacent andpartially wrapped (or in some instances substantially wrapped) aroundthe loop 400, e.g., configuration of loop 400 illustrated in FIG. 2A (orother suitable configuration of loop 400). More particularly, the shield408 is operably secured to and disposed at a distal end of the coaxialcable 516 adjacent the loop 400. Shield 408 may be secured to coaxialcable 516 by any suitable securement methods including but not limitedto soldering, brazing, welding, adhesives, etc. In the illustratedembodiments, shield 408 is secured to coaxial cable 516 by way ofbrazing. In certain embodiments, shield 408 may be monolithically formedwith the radiating section 518. In another embodiment, shield 408 may begrounded or secured to an internal portion of the shaft 520 of themicrowave antenna 512. Shield 408 may be made from any suitable materialincluding but not limited to materials that are conductive,non-conductive or partially conductive. More particularly, shield 408may be made from metal, metal alloys, plastic, ceramic, etc. In oneparticular embodiment, shield 408 is made from metal, such as, forexample, a metal selected from the group consisting of copper, silver,gold, platinum, stainless steel and titanium.

Shield 408 is configured to provide enhanced directionality of theradiating pattern of the electrosurgical energy transmitted to theradiating section 518 and/or conductive tip 524. In one particularembodiment, the shield 408 may include a generally hemispherical orclamshell configuration (FIG. 5). In another embodiment, the shield 408may be elongated having a generally triangular cross-sectionconfiguration (FIG. 6). In either instance, the shield 408 concentratesand/or directs the electrosurgical energy transmitted to the radiatingsection 518 and/or conductive tip 524 to the target tissue site.Examples of other suitable types of reflectors or shields (and operativecomponents associated therewith) are described in commonly-owned U.S.patent application Ser. Nos. 12/542,348 and 12/568,524 filed on Aug. 17,2009 and Sep. 28, 2009, respectively.

In the embodiment illustrated in FIG. 1A, the generator is shownoperably coupled to fluid supply pump 40. The supply pump 40 is, inturn, operably coupled to a supply tank 44. In embodiments, the supplypump 40 is operatively disposed on the generator 200, which allows thegenerator to control the output of a cooling fluid 42 from the supplypump 40 to the microwave antenna 512 according to either open and/orclosed control loop schemes. As can be appreciated providing the coolingfluid 42 (see FIGS. 2A and 3) to the radiating section 518 and/or theloop 400 increases the power handling capability of the microwaveantenna.

As noted above, in some instances it may prove useful to utilize amicrowave antenna (e.g., microwave antenna 100) that includes adeployable tip 114. In this instance, the deployable conductive tip 114includes a configuration of loop 400 proportioned small enough indiameter to facilitate deployment of the conductive tip 114. During asurgical procedure, e.g., ablation procedure, a portion of the loop 400may be positioned around a tumor or soft tissue.

In certain embodiments, a portion of the microwave antenna may be coatedwith a non-stick material 140 (see FIG. 1A, for example), such as, forexample, polytetrafluoroethylene, commonly referred to and sold underthe trademark TEFLON® owned by DuPont™.

In certain embodiments, a dielectric material 517 (see FIG. 2A, forexample) may surround the radiating section 518 and/or the loop 400 andreactive components associated therewith to achieve an impedance matchbetween the microwave antenna 100 and tissue to emit a radiating patternfrom the radiating section 518 of the microwave antenna 512.

Operation of system 10 is now described with respect to FIGS. 1B and 2.A portion of the microwave antenna, e.g., a radiating section 518 and/orconductive tip 524, is positioned adjacent tissue at a target tissuesite (or in some instances, a portion of the microwave antenna 512,e.g., a portion of loop 400, may be wrapped around tissue, e.g., atumor). In certain instances, a fluid 42 may be circulated through thefluid lumens 530 a and 532 a and around the radiating section 518, seeFIG. 2A, for example. Thereafter, electrosurgical energy is transmittedfrom the generator 200 to the radiating section 518 and/or conductivetip 524 of the microwave antenna 512 such that a desired tissue effectmay be achieved at the target tissue site. In accordance with thepresent disclosure, the loop 400 improves electrosurgical energytransfer from the generator 200 to the microwave antenna 512 and/or thetarget tissue site and allows the microwave antenna 512 or portionassociated therewith, e.g., radiating section 518 and/or conductiveportion 524, to be utilized with more invasive ablation procedures.

From the foregoing and with reference to the various figure drawings,those skilled in the art will appreciate that certain modifications canalso be made to the present disclosure without departing from the scopeof the same. For example, one or more modules associated with thegenerator 200 and/or controller 300 may be configured to monitor thereactive elements or components, e.g., inductive element 402, associatedwith the loop 400 such that a specific electromagnetic field isgenerated by the reactive elements or components during the transmissionof electrosurgical energy from the generator 200 to the microwaveantenna 512. More particularly, one or more sensors (e.g., one or morevoltage and current sensors) may be operably positioned at apredetermined location and adjacent the radiating section 518 and/orloop 400. More particularly, the sensor(s) may be operably disposedalong a length of the loop 400 and in operative communication with themodule(s) associated with the generator 200 and/or controller 300. Thesensor(s) may react to voltage and/or current fluctuations associatedwith the loop 400 and caused by electromagnetic fields fluctuationsgenerated by one or more of the reactive components, e.g., inductiveelement 402, associated with the loop 400. In this instance, thesensor(s) may be configured to trigger a control signal to the module(s)when an electromagnetic field of predetermined strength is generated.When the module(s) detects a control signal, the module may send acommand signal to the generator 200 and/or controller 300 such that theelectrosurgical power output to the microwave antenna 512 may beadjusted accordingly.

While several embodiments of the disclosure have been shown in thedrawings and/or discussed herein, it is not intended that the disclosurebe limited thereto, as it is intended that the disclosure be as broad inscope as the art will allow and that the specification be read likewise.Therefore, the above description should not be construed as limiting,but merely as exemplifications of particular embodiments. Those skilledin the art will envision other modifications within the scope and spiritof the claims appended hereto.

What is claimed is:
 1. A microwave ablation system, comprising: a powersource; a microwave antenna; a coaxial cable feed adapted to connect themicrowave antenna to the power source, the coaxial cable feed includingan inner conductor, an outer conductor, a dielectric shielding, and aradiating section; a reactively-loaded loop structure coupled to theinner conductor, the reactively-loaded loop structure having at leasttwo reactive components; and a conductive shield disposed adjacent adistal end of the radiating section and extending beyond the distal endof the radiating section to at least partially wrap around the radiatingsection.
 2. The microwave ablation system according to claim 1, whereinthe inner conductor defines at least a portion of the radiating section.3. The microwave ablation system according to claim 1, wherein at leastone of the at least two reactive components is selected from the groupconsisting of an inductor, a capacitor, and combinations thereof.
 4. Themicrowave ablation system according to claim 3, wherein the innerconductor includes a combination of at least one inductor and at leastone capacitor.
 5. The microwave ablation system according to claim 4,wherein the at least one inductor and the at least one capacitor aredisposed on the inner conductor in series with respect to each other. 6.The microwave ablation system according to claim 1, wherein the innerconductor includes a spiral configuration and capacitively couples adistal end of the inner conductor to the dielectric shielding.
 7. Themicrowave ablation system according to claim 1, wherein a dielectricmaterial surrounds the radiating section and at least one of the atleast two reactive components, the dielectric material providing animpedance match between the microwave antenna and tissue.
 8. A microwaveantenna, comprising: a coaxial cable feed including an inner conductor,an outer conductor, a dielectric shielding, and a radiating section; areactively-loaded loop structure coupled to the inner conductor, thereactively-loaded loop structure having at least two reactivecomponents; and a conductive shield disposed adjacent a distal end ofthe radiating section and extending beyond the distal end of theradiating section to at least partially wrap around the radiatingsection.
 9. The microwave antenna according to claim 8, wherein theinner conductor defines at least a portion of the radiating section. 10.The microwave antenna according to claim 8, wherein at least one of theat least two reactive components is selected from the group consistingof an inductor, a capacitor, and combinations thereof.
 11. The microwaveantenna according to claim 10, wherein the inner conductor includes acombination of at least one inductor and at least one capacitor.
 12. Themicrowave antenna according to claim 11, wherein the at least oneinductor and the at least one capacitor are disposed on the innerconductor in series with respect to each other.
 13. The microwaveantenna according to claim 8, wherein the inner conductor includes aspiral configuration and capacitively couples a distal end of the innerconductor to the dielectric shielding.
 14. The microwave antennaaccording to claim 8, wherein a dielectric material surrounds theradiating section and at least one of the at least two reactivecomponents, the dielectric material providing an impedance match betweenthe microwave antenna and tissue.